This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A187622 #6 Jul 22 2025 10:50:06 %S A187622 31,446,60,324452,70548,6090023738,720252796 %N A187622 Number of (n+1)X(n+1) 0..2 arrays with each 2X2 non-center subblock determinant nonzero and the array of 2X2 subblock determinants antisymmetric under 90 degree rotation. %C A187622 Column 2 of A187624 %e A187622 Some solutions for 4X4 %e A187622 ..1..2..0..2....2..2..0..2....1..1..2..1....1..2..1..1....2..0..1..2 %e A187622 ..0..2..1..2....0..2..2..2....2..1..1..1....1..1..1..2....1..2..2..0 %e A187622 ..1..2..1..0....2..2..2..0....1..1..1..2....2..1..1..1....0..2..2..1 %e A187622 ..1..0..1..2....2..0..2..2....1..2..1..1....1..1..2..1....2..1..0..2 %K A187622 nonn %O A187622 1,1 %A A187622 _R. H. Hardin_ Mar 12 2011